Production of natural gas from drilled wells often has associated liquid production. The liquids may consist of water, oil or hydrocarbon condensates in any combination. A free flowing gas well may, over time, accumulate liquids in the well bore that are not carried to surface due to flow rates that are insufficient to entrain the liquid and keep it moving out of the well. In these cases, the liquids will accumulate to the extent that they build up in the well bore and exert a hydrostatic pressure against the producing part of the underground formation. This build up of liquid will continue until the hydrostatic pressure from the liquid equals or exceeds the natural pressure of the producing formation, and all flow of gas and liquids from that formation are stopped.
Various methods of removing the liquids from the wellbore are well known and in use. One such method is “Plunger Lift”, whereby a freely reciprocating piston, or plunger, is operated in an intermittent or continuous fashion, allowing the plunger to fall through the accumulated liquid to the bottom of the wellbore and then return to surface, pushing the liquid ahead of it and clear of the wellbore. This way, the back pressure against the formation is reduced or minimized and the well produces at a rate closer to it's theoretical maximum.
Recent years have seen the development of two-stage or multi-stage plunger lift systems. These systems utilize a two or more plungers in a staged arrangement in a single well. There are one or more staging tools placed at intermediate intervals in the well such that a separate plunger operates in each discrete segment or stage of the well. The staging tools are designed to isolate the well into discrete sections or chambers, usually with a one-way valve arrangement that allows the lowest sections to sequentially move the liquids up the well into the next chamber without permitting fallback of those liquids. This sequential lifting of the liquids allows the well to operate with lower gas volumes than single stage plunger lift, thereby providing a wider range of applications.
Current designs of staging tools incorporate two areas where a seal must be established to prevent the backflow of liquids. One is the use of a one-way valve where the main flow of gas and liquids pass though on their way to the surface. Typically a ball and seat arrangement or similar arrangement is used. The second area that needs to be sealed is the annular area between the tool and the production tubing. This is commonly achieved by the use of an elastomeric seal.
The annular elastomeric seals currently in use may remain exposed to the tubing wall both during the process of setting the tool and on it's extraction. Some tools simply use a seal such as a swab cup fitted over a sleeve. Other known art employs a retractable seal which is essentially an elastomeric bushing which is expanded when the device is set in the well by means of a tapered shaft forcing the bushing against the tubing wall. Upon extraction, the tapered shaft is removed from the elastomeric bushing allowing it to collapse away from the tubing wall. Known problems with this latter art is the nature of elastomers to take a “set” after a period of time, whereby they do not return to their original shape after the force which was holding them in place is removed. In such cases the elastomeric seal remains exposed and potentially in contact with the tubing wall leaving it prone to damage upon extraction.
The object of the proposed invention is to improve upon the known art of staging tool design, specifically by providing a means of protecting an elastomeric seal upon withdrawal of the tool from the well. This invention eliminates the problems associated with seal damage on extraction, thus avoiding problems to associated equipment when damaged seal components fall into the well and reducing the need for costly and time consuming rebuild of the staging tool.